This invention relates to a method for discharging leakage water from guide vanes of a reversible hydraulic machine, more particularly, in which resisting torque of a runner against the leakage water and temperature of the runner can be properly maintained and a thin water film having a suitable thickness is formed on the inner surfaces of the guide vanes to prevent air from leaking into a casing of the machine at a time of fully closing guide vanes of the hydraulic machine which carries out, at this time, water surface depression operation in both cases of a power generation direction and a pumping-up direction.
In a conventional hydraulic machine provided with movable guide vanes, resisting torque of the runner of the hydraulic machine is reduced by the steps of fully closing the movable guide vanes at a time of a condenser operation or a pumping-up stand-by operation, supplying compressed air into a runner chamber located inside the guide vanes, and then rotating the runner in the air with water surface being depressed.
In the hydraulic machine of the type described above, sealing packings are provided to upper and lower ends of the guide vanes to positively reduce water leakage from the fully closed guide vanes into the runner chamber, but actually, some amount of leakage water is inevitable. The water leaked from the guide vanes adheres on the outer peripheral surface of the runner by a centrifugal force generated when the runner rotates and resisting torque is generated in case of idle running of the runner. In addition, the temperature of the leakage water rises due to agitation for a long time to thereby expand the runner, which fact may bring about dangerous contact between the runner and upper or lower cover for the runner.
With a conventional hydraulic machine, in order to obviate such dangerous contact, the leakage water was discharged into a draft tube by interconnecting the runner chamber and the draft tube through a discharge pipe or arranging a discharge pipe so as to connect a lower cover located between the runner and the guide vanes to the draft tube.
However, with a reversible hydraulic machine in which the runner is rotatable in opposite directions, when the rotating direction of the runner changes to the condenser operation or the pumping-up stand-by operation, pressures different in both cases due to the centrifugal force are applied on a point of the outer periphery of the runner and the discharge efficiencies of the leakage water are also different in both the cases. Namely, when the discharge pipe is designed suitably for a condenser operation, a relatively large amount of the leakage water is discharged in a case where the hydraulic machine runs as a pumping-up stand-by operation and a considerably thin water film will adhere onto the inner surface of the runner, thus becoming less effective for cooling it. For the reasons described above, air adapted to depress water surface in the runner chamber leaks into a casing through a side gap between the guide vanes, then an inlet valve of the hydraulic machine is opened, and the leakage air swells rapidly and rises into a penstock, thus damaging an intake gate provided for the penstock. Moreover, the fact that the water film having a considerably small thickness is formed on the surface of the runner adversely affects the cooling effect of the runner and the runner expands due to the temperature rise of the compressed air agitated by the idle running of the runner at the outer periphery thereof. Thus, the dangerous contact may occur between the runner and the upper or lower cover. Particularly, with a hydraulic machine characterized by a high head, since the runner is generally rotated with a high speed, the temperature of the leakage compressed air rises in a short time and the possibility of the dangerous contact will be considerably high.